Latency of anterior interosseous nerve and amplitude of compound muscle action potential of flexor pollicis longus by needle electrode

Abstract Background: Detection of normal latency of anterior interosseous nerve (AIN) and amplitude of compound muscle action potential (CMAP ) with needle elctrode in muscles innervated to this nerve is required in all electrodiagnostic laboratories. Objective: To determine normal latency of AIN and amplitude of CMAP in flexor pollicis longus (FPL) by needle electrode. Methods: This electrodiagnostic study was performed on 33 normal subjects (11 males, 22 females) aged 25-35 (group 1) and 36-45 (Group) at shiraz shahid chamran and Namazi hospitals from summer till fall 1998. This study was done by holding forearm in full supination, needle electrode (reference) was inserted in midway between elbow and wrist in the adjacent of radial bone in FPL muscle and groud electrode was placed on the posterior part of the forearm. The AIN was stimulated at the anterior of elbow, the respones was recorded and the results were analyzed employing T. test. Findings: The latency mean of AIN was 2.87 ms with standard deviation (SD) 0.49 ms, the maximum and minimum of lancy was 3.85 and 1.89 ms, respectively. The amplitude mean of CMAP of FPL was 4.73 mv, with SD of 2.61 mv. Since the obtained did not follow normal distribution pattern, its lowest limit of normal value on the basis of half of the mean was 2.36 mv, and based on log transformation it exceeded 1.69 mv. Conclusion: The normal values of amplitude CMAP and the latency of AIN in healty persons, can be helful distinguishing lesions AIN.